Electronic devices, including mobile computing and/or communication devices, are becoming smaller thereby driving the weight and size of data storage devices down, while requiring large storage capacity in the terabyte range and low power consumption.
A data storage device, for example hard disk drives (HDDs), employs a servo system for tracking and controlling the movement of the read/write head. The servo system performs two distinct functions known as the “seek” or “access” function and the “track following” function.
Conventional servo systems employ embedded servo where the servo information runs radially from the inner diameter (ID) to the outer diameter (OD) of the disc in a series of “servo wedges” interspersed with data. Therefore, the servo information is only detected when the read/write head moves over these servo wedges. In between the servo wedges, no servo information is received by the head. Servo information includes indexing information, for example, Sector Address Marks (SAM) and Gray codes are encoded within (and occupy the space in) the servo wedges of the embedded servo. In addition, conventional servo systems typically employs ABCD servo-burst-signal pattern.
Data storage devices also employ dedicated servo where the servo information is provided on a (servo) layer distinct from the data recording layer. The indexing information is difficult to store in the servo layer as noise from the recording channel corrupts this information.